TWO DISTANT HALO VELOCITY GROUPS DISCOVERED BY THE PALOMAR TRANSIENT FACTORY

Journal Article · Mon Aug 20 00:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/755/2/134· OSTI ID:22039079

Sesar, Branimir; Cohen, Judith G; Levitan, David; Kirby, Evan N; Kulkarni, Shrinivas R; Prince, Thomas A ^[1]; Grillmair, Carl J; Laher, Russ R; Surace, Jason A ^[2]; Juric, Mario ^[3]

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1. Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)
2. Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States)
3. Large Synoptic Survey Telescope Corp., 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

We report the discovery of two new halo velocity groups (Cancer groups A and B) traced by eight distant RR Lyrae stars and observed by the Palomar Transient Factory survey at R.A. {approx} 129 Degree-Sign , decl. {approx} 20 Degree-Sign (l {approx} 205 Degree-Sign , b {approx} 32 Degree-Sign ). Located at 92 kpc from the Galactic center (86 kpc from the Sun), these are some of the most distant substructures in the Galactic halo known to date. Follow-up spectroscopic observations with the Palomar Observatory 5.1 m Hale telescope and W. M. Keck Observatory 10 m Keck I telescope indicate that the two groups are moving away from the Galaxy at v-bar{sub gsr}{sup A} = 78.0{+-}5.6 km s{sup -1} (Cancer group A) and v-bar{sub gsr}{sup B} = 16.3{+-}7.1 km s{sup -1} (Cancer group B). The groups have velocity dispersions of {sigma}{sub v{sub g{sub s{sub r}{sup A}}}} = 12.4{+-}5.0 km s{sup -1} and {sigma}B{sub v{sub g{sub s{sub r}{sup B}}}} =14.9{+-}6.2 km s{sup -1} and are spatially extended (about several kpc), making it very unlikely that they are bound systems, and more likely to be debris of tidally disrupted dwarf galaxies or globular clusters. Both groups are metal-poor (median metallicities of [Fe/H]{sup A} = -1.6 dex and [Fe/H]{sup B} = -2.1 dex) and have a somewhat uncertain (due to small sample size) metallicity dispersion of {approx}0.4 dex, suggesting dwarf galaxies as progenitors. Two additional RR Lyrae stars with velocities consistent with those of the Cancer groups have been observed {approx}25 Degree-Sign east, suggesting possible extension of the groups in that direction.

• OSTI ID: 22039079
• Journal Information: Astrophysical Journal, Vol. 755, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTRONOMY
ASTROPHYSICS
ELEMENT ABUNDANCE
HYDROGEN
IRON
MILKY WAY
SUN
TELESCOPES
VARIABLE STARS
VELOCITY